1. Field of the Invention
The present invention relates to a method of detecting an abnormality in a photoelectric conversion element, an abnormality detection apparatus, and a system using the same and, more particularly, to a method and apparatus for detecting an abnormality without using a photoelectric conversion element serving as a standard, and a power generating system using the same.
2. Related Background Art
In connection with global warming owing to emission of CO.sub.2 and the like arising from the use of fossil fuels, and radioactive contamination caused by accidents in nuclear power plants and radioactive wastes, the earth environment and energy problems have rapidly become matters of great concern. Under the circumstances, solar cells as photoelectric conversions element using incident light are expected to be used worldwide as an inexhaustible, clean energy source. Solar power generating systems using this solar cell vary in type and scale, ranging from several W to several thousand kW, e.g., a system designed to store the energy generated by a solar cell by using a battery, and a system designed to supply output energy from a solar cell to a commercial use system by using a DC-AC converter.
FIG. 13 shows such a system as a comparative example of the present invention. In this solar power generating system, a solar cell array 1 is constituted by four parallel-connected solar cell strings 11, 12, 13, and 14 each consisting of a plurality of series-connected solar cell modules. The output from the solar cell array 1 is sent to a power conversion unit 2 including a control unit for performing maximum output control and then supplied to a load 3. In this case, the load 3 is an electric power system (e.g., the above commercial use system). A system for supplying electric power from a solar cell to an electric power system is called a system interconnection system, which is one of the optimal system forms using a solar cell as a general energy source.
In general, a solar light power generating system of this type includes various protection units for preventing electrical shocks and the like. However, not much effort has been made to develop methods of detecting defects in solar cell modules. As an example of such a defect detection method, the following conventional method has been employed. In this method, the conversion efficiency of a solar cell array is calculated by using, e.g., an expensive pyrheliometer and a power measurement unit, and an abnormality in the solar cell array is determined when the conversion efficiency is below a standard value.
In the above conventional method of detecting a defect in a solar cell module, a standard value for the conversion efficiency is fixed but cannot be properly set in accordance with the climate at a place where each solar cell module is installed. That is, since the output of a solar cell has a spectral and a temperature dependency, the conversion efficiency considerably varies. In addition, especially in a solar cell consisting of an amorphous silicon material, the photoelectric conversion element itself undergoes optical deterioration. This deterioration is greatly dependent on environmental factors such as the amount of solar radiation and temperature. Therefore, it is very difficult to obtain an accurate standard value upon consideration of these factors, the characteristics of each solar cell, and the like.
As a means for accurately determining a standard value, only a process of making a standard measurement at the installation site and checking the power generation performance at the corresponding the installation site is available. This, however, requires enormous cost and time. In order to solve this problem, a standard module may be installed independently of the solar cell array. However, it is irrational to install a solar cell which does not contribute to power generation. In addition, if the standard module breaks down owing to a failure or the like of the system, no means of obtaining an accurate standard value remains. Furthermore, a measurement error may occur between the solar cell array for power generation and the standard value module.
In the above method, whether the overall solar cell array is defective is determined on the basis of a standard value. Therefore, even if an abnormality is determined, a cumbersome operation is required to find a specific defective part of the solar cell array. For this reason, it takes much time and labor to repair a solar cell array or replace modules.